Michael Mesnier <mmesnier@xxxxxxxxxxx> wrote:
Hello,
Please cc: me directly in your response.
I'm running into some trouble with an installable file system I'm writing. In myfs_readpage() I simply return block_read_full_page() which subsequently calls myfs_get_block(). However, there's a delay before the I/O actually gets issued to the device. Running sync from the command line causes the I/O to get issued immediately, so the sync call (even it there aren't dirty buffers) also manages to schedule any outstanding read I/Os. How should my fs indicate to the vfs that these read I/Os need to be issued immediately after my_readpage() is called?
Normally we leave the I/O pending in the expectation that more readpage()
requests will occur. This allow us to merge things in the disk request
queues. We'll actually submit the I/O to the device if:
a) There's a lot of it pending or
b) There haven't been any more readpage() calls for a while or
c) Someone actually wants to wait on the I/O (say, via lock_page())
It is unusual that you want this I/O to kick off immediately. You will
probably find that blk_run_backing_dev() will do what you want.
That's all for a 2.6 kernel - you didn't specify. It it's a 2.4 kernel
then you'll need to use run_task_queue(&tq_disk) to flush the queued I/O
requests.